Boschitz, E.

Chabre, Marc

Hendrie, D.L.

Pugh, H.G.

eScholarship - University of California

Lawrence Berkeley National LaboratoryRecent WorkTitleHIGH-RESOLUTION STUDY OF TEE C12(p,2p)B11 REACTION AT 50 MeVPermalinkhttps://escholarship.org/uc/item/1365427qAuthorsPugh, H.G.Hendrie, D.L.Chabre, Marcet al.Publication Date1965-02-01eScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaUCRL-11940 University of California Ernest 0. Radiation lawrence Laboratory TWO-WEEK LOAN COPY This is a Ubrar~ Circulating Cop~ which ma~ be borrowed for two weeks. For a personal retention cop~. call Tech. Info. Diuision, Ext. 5545 HIGH-RESOLUTION STUDY OF THE c 12(p, 2p}B11 REACTION AT 50 MeV Berkeley, California DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. ·• .. '· ·-:: -·. ._,·· ·· ...... ~ .... ;_ ·---.' .·_,·· - ~- . ; : ( .. ·<' ·:. UNIVERSITY OF CALIFORNIA Lawrence Radiation Laboratory Berkeley, California AEC' Contract No. W-7405-eng-48 ·'·, ·, .·.··",(·~.: :·:; ·'·, -·:-, ·. ··_.· ·, .-UGRL-11940 / :~ ' ~ . ' . ;· .• .. ·.·; ·' .v ' ' .. .... -··' . ·HIGH-RESOLUTION STUDY OF THE c12(~,2p)B11 REACTION AT 50 MeV . ·• ·, '1 '. ,.-. H. G. Pugh, D ... L'. Hendrie, Marc Ghabre, and E. Boschitz ~. :. ' ·. . : ~ ' . '' .. · ;.,_. · .. · ..FebruarY 1965 >' · .... __ ' '··:'· . ,. ,· I " I 'i .. · . . I i ·_!._,:: ... _: . : ·.';: ~--..... . . . ~. ',.:· : .. -·· . ;. ' : ~ ·- .. :. ··:·:, __ :_ ,i·. .. ·. ~: ,.. .. '•i' . '·, 'I : .~ . : ~-· .. -~~ :-1 . ' ' ~~ ',,I I '\• j·:, i, •' .i·(·.'! ,· UCRL-11940 HIGH~RESOLUTION STU.DY OF THE c12(p,2p)B11 REACTION AT 50 MeV* :· .H~ G·.>Pughy D~, L. ·Hendrie~· Marc Chab~et, and E.' ·Boschiiz* Lawrence Radiation Laboratory. University of California · Berkeley, California February 1965 ' . The (p,2p) reaction has been extensively studied at energies between . 1 40 MeV and 440 MeV. These studies have given valuable information on the gross shell structure of nuclei but difi'iculti~s in obtaining good energy resolution have limited the use of.the reaction for detailed spectroscopic investigations. We ·have studied the. c12(p, 2p )B11 reaCtion at 50 .MeV using solid state . . counters for detedion of the outgoing protons and· .. have; for the first time in this type of reaction, ·Obtained ~nergy resolution sufficient to distinguish· between individual states of the final nucleus. '-..' · A carbon target was bombarded with 50 MeV protons from the Berkeley 88-inch cyclotron. Proton pairs from· the· (p, 2p) reaction. were detected in two counter telescopes, each consisting of' a pair of lithium-drifted silicon de-tectors: a 0.024 inch 116E 1.1 detector and;a 0.120 inch "E" detector. The cir-.. I cular collimators defining each s-olid an~le subtended 6.9 ·x 10-3 steradians at the target .. Electronic circujts selected only those events in which the outgoing particles, identified as protons with energies between 9 MeV and 25 MeV, produced a fast coincidence ~etween>all :four counters. The resolution of the summed energy spectra ( the total energy deposited in all four detectors) .. · was better than .350 keV. Figure l(a) shows a summed energy spectrum whi,ch is 11 fairly typical and illustr'ates that the· transition to the ground state of B ~s predominant~ We have meas1.,1.red a~lar corre·lations for. this transition with· the telescopes placed at equal angles, e, on opposite sides of the incide.nt beam direction. i .. ··'· .. .·· ... ;,·, \·.1·1 :__ ____ __;_ ________ .:.__~ _____ :_ _____ . __ ._ ------~-,·,li' I ' ·'I I! , 1;. I -2- UCRL-119L~O. Figure 2 shows the differenti~l cross-section for the ground-state transitior as a function of e for events in vihich I El - E21 <5 MeVJ where E1 and E2 are.the energies of the two detected protons. This angular corre-lation, differs .... 'markedly from those obtained at higher energies: I. a) rhere are more oscillations} presumably diffraction effects due to . localization of the interaction in the nuclear•surface. b.) Tpe c~oss·-sectio~ rises· quickly at -small anglesJ ·possibly due to the r_apid rise of the proton-proton scattering cross-section at .low energies. Recent distorted wave calculations seem to r:eproduce the major features of the 1 . 2 corre at~on. The 'inset in· .Fig. 2 shows three spectra ;:t;. (E1 - E2 ) for the ground-. state transition. The absence of sharp structure in these spectra (which as . . a consequence of our geometry must be s~etrical about E1 = E2 ) indicate~ that the reaction does not proceed through long-li ve_d proton-unstable excited 'states of c12 . The (Ei -. E2 ) spectra .do J howev~r.J ~show slowly-varying structure p.ear the minim~ of.· the angular correlation. )At these points'. the cr~ss-s~~tion \ averaged ove~ I E1 - E~ I< 5 MeV. is not a 1 good. approximation to that for· equ.al .. energy sharing. There we have dr'aW:n·smooth· lines through the. spectra to obtain the cross-section for Ei = E 2 ;: the results ar~ given by the dashed line in •· Fig. 2. The effects. of angular resolutio.n on the angular correlation have not , .· been extracted. It will be seen from Fig. l(a) that four excited states of B11 are . particularly interesting sinceJ in order for them to be produced by simple. . ' \ . 12 . . 12 removal of a proton.from C ) it is necessary for the C .ground state to · contain large admixtures ·of 1±.· particles. vlhile calculations do indicate the . / :: ' ''.1 ~ •. .• ' .. \ ' ' II ·,:;\1 ...... :\_·,:-~~ .• -3- UCRL-ll940 presence of 1 f admixtures in c12 it is by no means clear whether the quantity is sufficient.3 Alternatively it is tempting to consider the possibility that these four states may have the character of a p3; 2 proton hole coupled to the 2+ first excited state of c12 at 4.43 MeV. Their formatio~ would the~ naturally proceed through a double excitation process, i.e., pickup of a p3; 2 proton accompanied by inelastic scattering of either the incoming or one of the out-going protons. :. This mechanism is plausible since the 4; 43 MeV state in c12 tp.: ·is known to be strongly excited by inelastic proton scattering at these energies. _Double excitation processes of this type have been suggested by Penny and Satchler5 ~d have re~ently. been invoked .to .inte:r:-pre_t an anomalous angular dist~ibution in the cr52(d,p) reaction. 6 The production of the-l/2- state at 2.14 MeV would be enhanced by_ simple removal of a proton from the (p3; 2 ) -~ 2 . ~ (p1; 2 ) admixture present in the ground s~ate of C . We might also expect _ significant configuration mixing between the 3/2-:- excited state and the ground.· state. Using the same counter telescopes as for the (p,2p) reaction we have also studied the c12(p,d)c11 reaction wi~h comparable e~ergy re~oluti~n-, pro-ducing analog st.ates in the. mirror- nucl~us,' Figure l(b) shows a spectrum: for this reaction,· The relative populations of th,e corresponding states in the .. : -two reactions are comparable. In particular the relative weakness of· the transition to:_:the 6.34 MeV level in the (p,d) reaction supports. our assillnpti'on that the unresolved doublet at 6;8 MeV in B11 for the (p,2p) reaction consists '. :· ·-: .. ,;: mainly of the 7/2- state. The 5/2- and 7/2- states have novf been observed ·in a variety :Of' -single_-- 12 .· . . 7 nucleon pickup reactions on C ~p to 150 MeV. Clarification of the role of ' the double-excitation p~ocess· in these reactions is necessary to enhance their usei'ulnes:;;.as spectroscopic tools. \··' ..i.: :':. ·" . ' l.l .' ', I ~ . -4- UCRL-11940 We wish to thank W. R. Gibson, A. R. Johnston and R. J. Grif~iths8 for sending us their results prior to publication. There seems to be no direct comparison that can be made between the two sets of results • . REFERENCES l. ·H. Tyren, P; Hillman and Th. A. J. Maris, Nucl.. Phys. 1' 10 (1958); G. Tibell, 0. Sundberg and P. U. Renberg, Arkiv ftlr Fysik 25, 433 (1963); · M. Riou, Proceedings of the Gatlinburg conference, O~tober 1964, (to be ·. published). 2. K. L. Lim and I. E. McCarthy,. Phys. ,Rev. 133, Bl006 (1964) and private conununication. 3·. A. Goswami and M. K. Pal, Nucl .. Phys,· 44, 294.(1963).· . . . . 4. R. ·w .. Pee1le, Phys: Rev. 105,1311 (1957); T. Stovall and N. M. Hintz, Phys. ReV<_ 135, B330 (1964).· 5. S. K~ Penny and .G. R. Satchler, Nucl.: Phys. 53, 145 (1964). 6. R .. Bbck, H. H. Dohni, R. Rildel and R. Stock, Phys. Letters 13, 151 (196.4) .. 7· . .. I W; H. Kelly, c ... A. Ludemann and C. D. 'Goodman, Bull,. Am •. Phys. Soc. 10,-. ! I . . i' ' 121 (1965);. . ' •,. .! C. Detraz, Ph. D. Thesis., Or say ( 1964) ;.·. S. M .. Aust.in, G. L. Salmon,. A. B. ·::Clegg, K. J. Foley ·and D. Newton} Proc. Phys. Soc. (London) 80, 383 (1962); · . J. W. Watson, F. 'Ajzenberg-Selove and R. Middleton, Bull. .Am •. Phys. Soc. 10, 9 (1965). 8. · R. · J. Gr~ffiths, A: E. ·McCiatchie, W. R. Gibson, S. J. Hall, A. R. Johns.ton · ·. and K. M. Knight, Congres International de· Physique Nucleaire, Paris, .·3a(l)/c9) .(1964); . ' W. R. Gibson,. A. R. Jqb.ilston and R. J. Griffiths, (to be published). · ... : :,·. 0. -5- UCRL-11940 FIGURE CAPTIONS - 12 11 Fig. 1(a). A summed energy spectrum (E + E ) for the C (p,2p)B reaction 1 2 at 50 MeV. The positions of known excited states of B11 are.indicated. 1( b). A deuteron energy spectrum f~om. the c12(p, d)C11 re~ct:i.on at 50 Me~. 11 ·. The positions ·of known excited states of C are indicated. Fig. 2. 'The differential cross-section dcr/an1 an2 d(E1 - E2 ) for the c12(p 2p)B11 . reaction at 50 MeV as ·a functibn of e. The cross-' g. s. ''.. section has been averaged over the region IEl - E21< 5 MeV indicated .b~ the vertical_dotted lines on -the (E1 _:.. E2)_ spectra·shown in the-inset. .The dashed. line. is an· approximation to. the cross-section for equal sharing of energy between the outgoing protons, obtained as I ·. ~ described in the text. o( .. \ ... . FOOTNOT-ES. ' . / ' ( ·' .·.·· '* . . . . . _ . Work performed under the .. aus.pices of· the· U. · S. Atomic Energy Commission. . . . . . ' . t . 0 • 0 · NATO Fellow on leave froni CNRS, Institwt Fourier, Grenoble, • • j • J :j: 0 • • • 0 0 ••• ' i' On leave from NASA Lewis Research Centef., .Cleveland, Ohio; ·. I ,. . '~ .' • 0 ' · .. ' '··· .. ...... '.•. , .. ,·' I I ', :' -~ . . ' ,. ' . · .. \ . ;., ..... ........ ··· ._: ... ,. France. . , .. · . ,;'•' '' .. · •, .··' . . ~ . . .. ~ . . ' . ·.-) 3: c CD u. 0 ~· CD() ::r 0 ::J ::J CD 0 Counts p_er channel 0 0 / .,. ---'· I\) 0 0 Cl -Q. (\) <l>:;' II N 0)"0 ..,..---- 7.30 MeV (5/2-) Ul -__ ... . 0 OJ . ,_.---6.81MeV (112+,3/2+) -' ---' 6. 76 MeV. 712-0'1 / o, :s;: ([) < ----5.04 MeV (3/2-) ----4.46 MeV 5/2-----2.14 MeV 1/2-... O!.gOJ ' . -Kl !J) -I :, ~ . ·o .. -' 0 0 0 .I ' . /"' 1\) 0 0 0 ---'-:--6.90 MeV (-) --- 6.48 MeV ( 7/2-) ~--6.34 MeV CT () Cl) iii g-cr "'0 nO. .[\)-(.;\!(') 0 -·Ul 0 :s;: ([) ----4.81 MeV (3/2-) < ----4.32MeV i 5!2-------1.99MeV 112-. t (.:.! <0 (') ~-. ln = I ,. .. ! ',~~ ~'s ··~ ·-:', ~:.c··~J .. --*---~ f .. -' C\/1 w w ........ 30 15 I L 12 8 4 o -4 -a -12. 12 8 4 ·· o -4 -s -12 ' I \111111111\i' 11111111111)11 ulllull .I I J ' ' I 12 8 4 0 -4 -6 -12 E 1 - E2 (MeV) e =25° . o~~~~--~~~~--~~~~~ ·. 0 20 40 60 80 100 120. B (deg) . MUB·5057 . \' . . ' . .. ~\ ' ~·· . .. .. .. , This report was prepared as an account of Government sponsored work. Neither the United State~, nor the Com-mission, nor any person acting on behalf of the Commission: A. Makes any warranty or representation, expressed or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this report; or that the use of any information, appa-ratus, method, or proriess disclosed in this report may not infringe privately owned rights; or B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of any infor-mation, apparatus, method, or process disclosed in this repor:t. As used in the above, "person acting on behalf of the Commission" includes any employee or contractor of the'Com-mission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, disseminates, or provides access to, any information pursuant to his employment or contract with the Commission, or his employment with such contractor . 

HIGH-RESOLUTION STUDY OF TEE C12(p,2p)B11 REACTION AT 50 MeV

Abstract

Similar works

Full text

Available Versions

eScholarship - University of California